Vacuum requirements
 

On my M103 I have 15hg. Shouldn't it be higher? Realizing there are several causes for low vacuum, Ign timing low, leaks, plugged cat etc. Question is, how low does vacuum have to go before it affects transmission shift points and 'other' functions?

15" vac is about right.

Anything below 12" will start causing problems.

Look for leaks before you start on timing, etc, including the idle control valve if you have one.

Peter